1. Technical Field
The present invention relates a method for monitoring the amount of moisture sprayed across the width of moving material webs for moistening them over their width, a device for executing the method and the use of this device.
2. Background Art
In the graphic industry it is necessary to moisten rapidly moving paper webs during defined stages of processing, for example after they have been moved through a dryer for the drying of printing ink. The moisture can either be applied by means of a roller on which a liquid is sprayed, or by directly spraying the liquid on the rapidly moving paper web. In the process, the liquid is sprayed by a spraying device over the width transversely to the moving direction of the paper web, so that the entire width of the material web is moistened by the liquid. This technique for applying liquids has also proven itself in the textile, foil, non-woven, wood, tissue and other industries. A device for such moistening is known from DE 42 27 136 C2, for example. By means of such a device it is possible to moisten material webs evenly, and liquids of higher concentration and reduced water content can be applied to the material web. The spraying technique used permits a contactless and even application over the entire width of the material web without the formation of drops, so that gentle and tension-free material processing is provided and therefore the material structure is maintained.
Problems arise if the spraying device does not operate correctly, for example if one of the several spraying devices arranged next to each other to cover the full width of the material web does not operate correctly or even breaks down. In this case the material web is not correctly moistened, or even not moistened at all, in this area, so that the material web passed along the spraying device has strips which have been differently moistened. Since the moisture content of the material web, and therefore the incorrect moistening, can only be detected much later in the processing in a step, downstream of the spraying device, and since the material webs are conveyed at very high speeds in the range of 10 m/sec, great lengths of the material web are very rapidly insufficiently moistened or even unusable. Known methods for monitoring moistening therefore require very large amounts of material and are highly cost-intensive.